diff --git a/affine/__init__.py b/affine/__init__.py
index 934fd13..caaca8f 100644
--- a/affine/__init__.py
+++ b/affine/__init__.py
@@ -368,8 +368,9 @@ def _scaling(self):
         det2 = (a * e - b * d) ** 2
 
         delta = trace**2 / 4.0 - det2
-        if delta < 1e-12:
+        if delta < self.precision:
             delta = 0.0
+
         sqrt_delta = math.sqrt(delta)
         l1 = math.sqrt(trace / 2.0 + sqrt_delta)
         l2 = math.sqrt(trace / 2.0 - sqrt_delta)